1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a channel allocation method for radio data calls having different bandwidths to each other.
2. Background of the Related Art
In a mobile communication network, a call connection of a mobile subscriber is typically performed by a call processing unit of a mobile switching system. The call processing unit discriminates and processes a voice call and a data call according to a service option of a call. The traffic of the voice call is transmitted in a 64 Kbps PCM (Pulse Code Modulation) method, while the traffic of the data call is converted to a frame relay mode, and processed by being interworked with an Interworking Function (IWF) of a data network.
FIG. 1 illustrates a call processing structure between the mobile switching system 10 and the IWF 20. When a call set-up request is inputted from a mobile subscriber, a call processing unit 11 determines whether it is a voice call or a data call according to a service option of that call. If the call is determined to be a voice call, the call processing unit 11 transmits the voice call to its destination through a relay line processing unit 14 to a PSTN (Public Switched Telephone Network) network. If, however, the call is a data call, the call processing unit 11 outputs the service option of the corresponding call and its related parameters to a frame relay converting unit 12, and requests that the frame relay converting unit 12 connect a traffic path to the IWF 20.
Upon receipt of the request for a traffic path connection from the call processing unit 11, the frame relay converting unit 12 converts the traffic of the 64 Kbps data call, that is, the traffic transmitted in the PCM method, to a frame relay mode. The frame relay connecting unit 12 then transmits the traffic to the IWF 20. The traffic of each data call thusly converted to the frame relay is sequentially multiplexed to an H0 channel of an E1 link and transmitted to the IWF 20.
The IWF 20 then determines whether the data call outputted from the frame relay converting unit 12 is transmitted in a circuit switching system or in a packet switching system. If the data call is to be transmitted in the circuit switching system, it is transmitted in an ISDN PRI (Primary Rate Interface) method through the PSTN path processing unit 13 of the mobile switching system 10 to the PSTN network. If, however, the data call is to be transmitted in the packet switching system, it is directly transmitted to a PSDN (Public Switched Data Network).
FIG. 2 is a diagram showing a construction of a related art frame relay converting unit of FIG. 1. The frame relay converting unit 12 includes a plurality of selves (self1˜selfn). 15 control boards, each having 8 time slots, and two control boards, each having 5 H0 channels, are mounted per single self. That is, each self includes total 120 time slots (64 Kbps) and two E1 links each having five H0 channels (384 Kbps).
Referring to FIG. 3, the operation of the related art method of channel allocation will be described. First, a data call connection request is received from the call processing unit 11 (Step S31). The frame relay converting unit 12 then allocates an available time slot (Step S32). At this time, since each self (self0˜selfn) includes total 120 time slots (64 Kbps), 120 data calls can be accommodated altogether.
When a time slot is allocated, the frame relay converting unit 12 allocates the H0 channel on the E1 link corresponding to the time slot, and assigns DLC (Data Link Connection Identifier) values sequentially or in a round-robin method, thereby allocating a plurality of data calls to the H0 channel (Step S33).
Accordingly, when only an IS (Interim Standard)-95A based data call is supported, the data call has a maximum single bandwidth of 13 Kbps due to the bandwidth limitation of a wireless interval. Thus, in order to guarantee a quality of data service, a maximum of 30 data calls can be allocated to a single H0 channel. Each data call is discriminated by DLCI values (DLCI0˜DLCI119) in the same channel.
As the H0 channel and the DLCI value are assigned on the E1 link, the frame relay converting unit 12 stores channel state information (Step S34), and converts the traffic transmitted from the allocated time slot to a frame relay and transmits it through the E1 channel to the IWF 20 (Steps S35, S36).
FIG. 4 show a sequential channel allocation for data calls having a single bandwidth to each other in accordance with the related art.
The method of sequential channel allocation according to the related art has various problems. For example, as described above, for the purpose of interworking with the IWF, the channel allocation on the E1 link is performed whenever a call is requested. For radio data calls according to IS-95A having a single bandwidth (13 Kbps) as shown in FIG. 4, since the number of occupied DLCs, that is, the number of data calls, signifies an occupied bandwidth, no problem arises with respect to channel allocation.
However, in the related art sequential channel allocation as shown in FIG. 4, when a new data call is requested after a third H0 channel is allocated, even though there is a H0 channel which does not go beyond the service quality guarantee limitation, a fourth H0 channel is allocated. Thus, channel congestion occurs and the call is delayed. This phenomenon becomes more serious where a middle-speed service and an high-speed service, such as the IS-95B and the IS-95C, having different bandwidths (64 Kbps, 128 Kbps) are supported together.
Accordingly, the related art sequential channel allocating method, which considers only the number of data calls without counting the bandwidth, causes a traffic delay due to traffic congestion. This results in a waste of the channel resource and a deterioration of capacity to accommodate subscribers.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.